Determination of ventilatory thresholds using near-infrared spectroscopy in trained recreational endurance and CrossFit® athletes

This research evaluated the accuracy of near-infrared spectroscopy (NIRS) measurements to determine ventilatory thresholds (VT) or critical power (CP) based on muscle oxygenation and assesses the device’s consistency across two constant load tests. Data from two cross-sectional studies involving trained recreational endurance athletes (26 from study 1) and CrossFit®
athletes (59 from study 2) were examined. Incremental ramp tests on a cycle ergometer were performed and followed by either a constant load test (study 1) or a CP test (study 2). When comparing power output or heart rate between NIRS-derived breakpoints and VT weak to moderate agreement was found. Mean differences in power output and heart rate ranged from 16.8 to 22.4 W and 3.8 to 6.0 bpm at the first threshold and 27.4 to 31.2 W and 7.1 to 7.8 bpm at the second threshold. Comparing with CP, mean differences ranged from -0.4 to 0.4 W and -0.6 to 0.9 bpm. Test-retest reliability showed moderate agreement with a mean bias of 1.2 percentage points between constant load tests. Thus, NIRS may not be accurate for determining VT or CP during exercise due to limited agreement in power output or hear rate, notable variability on individual level and moderate reproducibility.